High temperature apparatus



Oct. 5, 1965 J. R. MORLEY 3,210,454

HIGH TEMPERATURE APPARATUS Filed May 17, 1962 2 Sheets-Sheet l POWDER INERT GAS SUPPLY WATER COOLING FOCUS P OQA'IER SUPPLY POWER SUPPLY D.C. GROUND VACUUM PUMP INVENTOR. JOHN R. MORLEY 24/0 0 -QZW ATTORNEYS Get. 5, 1965 I J. R. MORLEY 3,210,454

'HIGH TEMPERATURE APPARATUS Filed May 17, 1962 2 Sheets-Sheet 2 FIG. 2

IN VEN TOR.

JOHN R. MORLEY BY 70w mum ATTORN EYS United States Patent 3,210,454 HIGH TEMPERATURE APPARATUS John R. Morley, North Billerica, Mass, assignor to Alloyd Electronics Corporation, Qambridge, Mass, a corporation of Delaware Filed May 17, 1962, Ser. No. 196,041 3 Claims. (Cl. 131) This invention relates generally to high temperature heating devices using an ionized gas discharge and more particularly concerns a new and improved apparatus for melting and refining various materials of a refractory nature, such as powdered metal or the like, to form a molded article therefrom such as a solid metal ingot.

Heretofore, in heating refractory materials for the purpose of melting, welding, etching and the like, electron guns have been employed to direct a concentrated beam of electrons against a work piece within a highly evacuated chamber. The cathode emitter normally is in the form of a wire filament connected to a high voltage source with the thermionically emitted electrons focused by an electrostatic and/or electromagnetic lens system against the workpiece. In practice, a vacuum on the order of mm. Hg to 10- mm. Hg is required for proper operation of the apparatus. The equipment which is needed to obtain and maintain a vacuum of this level is both complex and expensive. Also the conventional cathode emitter or gun and its high Voltage power supply are relatively expensive pieces of equipment to manufacture.

When an apparatus of the above sort is employed to form ingots from a powdered refractory material, some rather complicated feeding devices have been utilized to deliver the powder to the ingot forming mold at the focal point of the electron beam.

Accordingly, it is a general object of the present invention to provide improvements in high temperature heating devices.

Another object of this invention is to provide an improved apparatus for generating and directing an electron discharge against a workpiece at a low voltage.

Still another object of this invention is to provide a novel powder melting and mold forming apparatus of the sort in which a thermionic emitter is mounted together with a mold within an evacuated chamber.

Yet another object of this invention is to provide means for facilitating the delivery of powdered material into a mold mounted within an evacuated chamber.

More particularly, this invention features an apparatus for heating melt stock by means of extracting and focussing electrons from an ionized gaseous discharge and directing them against the melt stock. In this invention, the gas is passed through a tubular cathode which, when energized, ionizes the gas by reason of thermionic and secondary emissions. Electrons from the resulting ionized discharge are focused onto the melt stock which may r be received in a mold. As another feature of this invention, the axes of the ionized discharge and the mold coincide but are oriented angularly with respect to the vertical to permit the powdered melt stock to be gravity fed into the mold from a location some distance above.

But these and other features of the invention, along with further objects and advantages thereof, will become more readily apparent from the following detailed description of a preferred embodiment of the invention, with reference being made to the accompanying drawings in which:

FIG. 1 is a schematic view of an embodiment of the invention, partly in sectional side elevation and partly in electrical and mechanical block diagram, and,

FIG. 2 is a top plan view thereof.

Referring now to the drawings, the reference character 10 generally indicates a cylindrical tubular housing of a 3,210,454 Patented Oct. 5, 1965 ice suitable material such as stainless steel or the like. The housing 10 includes a removable domed cover 12 which is formed with a relatively large central flanged port 14 and two smaller ports 16 and 18 angularly disposed on the dome 12. A pair of viewing ports 20 and 22 are located one on either side of the chamber 10 and a dis charge port 24 is located in the front wall of the chamber for connection with a vacuum pump 26 for evacuating the housing 10.

The entire housing 10 is supported by a base 28 to a platform 30 and it will be noted in FIG. 1 that the 1ongitudinal axis of the housing is tilted at an angle of about 20 with respect to the vertical. The reason for mounting the housing in this manner will become apparent during the course of this description. Mounted coaxially with in the housing 10 is an annular, water-cooled mold 32 supported on the bottom wall of the housing by an elon gated stand 34. Both the mold 32 and its stand 34 define a central passage to accommodate a retractable seat 36 mounted on the upper end of a feed screw 38 which, in turn, is in threaded engagement with a bracket 40 secured to the bottom wall of the housing. The seat 36 constitutes the bottom of the mold 32 and supports the lower end of an ingot 42 which is formed in the mold.

It will be noted that the port 18 is located directly above the mold 32 so that the melt stock, typically powdered metal, may be dropped by suitable metering device directly into the mold.

Coaxially aligned with the mold 32 and mounted in the port 14 is a gas ionizing device 44 comprising a watercooled tubular conduit 46 connected through a needle control valve 43 to a supply of pressurized inert gas 50 such as argon, helium or nitrogen. Mounted on the lower end of the conduit 46 by means of a heat conducting annular copper block 52 is a refractory metal tube 54, perhaps 3 in length and perhaps to /8" in diameter. The tube 54 serves as the cathode for an electron emission circuit and may be formed from a suitable material such as tantalum, tungsten, rhenium, molybdenum or the like in diameters of perhaps to /8".

The cathode 54 is electrically connected to an AC. power supply 56 capable of generating an RF output across the cathode and anode 42. The cathode itself is also connected to a DC. power source 58 preferably in the range of 30100 volts and typically maintained at about 50 volts negative with respect to the anode, which in this case is the ingot 42, and which is at ground potential.

In practice, to establish the discharge between the cathode 54 and the anode 42, RF power is applied between them thus causing the gas to ionize and a discharge is established when the DC. voltage is applied to the cathode. Ions are attracted to the cathode and cause it to become heated. When the cathode reaches a temperature at which the work function for electron emission is exceeded, electrons are thereupon thermionically emitted from the surface of the cathode. The emitted electrons are accelerated towards the anode and impinge upon the molecules of gas which is admitted through the conduit 46. The gas becomes ionized by the emitted electrons and an ionized discharge is completed to the ground potential ingot 42. The discharge, once started, is maintained across the electrical field between cathode and anode, and is characterized by a blue glow. The RF power supply may be deenergized once a steady discharge is established since the RF heating serves only to start the discharge.

Electrons from the ionized discharge are focused into the mold 32 by means of a magnet coil 60 mounted about the housing 10 and having a magnetic field that is coaxial with the axis of the discharge. Preferably the coil 60 comprises one pair of Helmholtz coils which provides a more nearly uniform magnetic field, particularly along its center axis, than that of a single coil and is much more compact than a conventional long coil. The coil is capable of developing a typical flux density at its center of about 100 gauss (.01 Weber).

The gas is delivered through the conduit to the ionizing zone at a controlled rate of flow which may range from to 50 atm. cc./min., for example. The resulting electron discharge, being focused into the mold 32 and being at a very high temperature, reduces to a molten state the metal in the upper end of the ingot 42. It will be understood that the mold is continuously fed with melt stock in powdered or granular form from the port 18 which is located directly above the mold 32. As the melt stock is added, it becomes molten and any entrained gaseous impurities are vaporized. Simultaneously the feed screw 38 is rotated either manually or automatically to retract the ingot 42 as its length is increased by the addition of melt stock. The cooling coils in the mold act to recrystallize the material into a solid ingot as shown in FIG. 1.

The apparatus disclosed herein provides a number of advantages notpreviously available in devices of this sort. For example, both the hollow tubular cathode and its low voltage power supply are considerably less expensive to manufacture than electron emitters and high voltage power supplies of conventional design. The cathode readily lends itself to thermal excitation by a relatively low RF power level which need be applied only long enough for the ionized gas discharge to complete the DC. circuit. It has been found that a system of this sort has a higher pressure requirement than a conventional electron beam melting apparatus. The arc discharge functions in a vacuum between 10" and 5 10- mm. Hg. This reduction in vacuum requirements is significant particularly because of the heavy cost of high vacuum pumps. By reducing the vacuum demands the expense involved in providing the equipment for achieving the vacuum is also reduced.

While the invention has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skilled in the art and that the foregoing description of the invention should be taken in an illustrative rather than in a limiting sense.

Having thus described my invention, what I claim and desire to obtain by Letters Patent of the United States 1. A high temperature furnace, comprising means providing an evacuated chamber, support means for mounting a workpiece Within said chamber, an electron emissive tubular cylindrical element mounted within said chamber and in line with said workpiece, means for delivering a flow of gas through said element, first circuit means providing an RF current to heat said element for first ionizing said gas, ions from said ionized gas causing further heating of said element to a point producing thermionic emission, and second circuit means providing a DC. potential between said element and said workpiece to produce a discharge of the ionized gas, said ionized discharge thereby completing a DC. circuit with said workpiece and simultaneously elevating the temperature of said piece.

2. A high-temperature furnace, comprising means providing an evacuated chamber, support means for mounting a workpiece within said chamber, a tubular element of emissive refractory material mounted within said chamber and in line with said workpiece, means for delivering a flow of inert gas through said element, first circuit means providing an RF current to heat said element for first ionizing said gas, ions from said gas causing further heating of said element to a point producing thermionic emission, second circuit means providing a DC. potential between said element and said workpiece to produce a discharge from the ionized gas, said ionized discharge thereby completing a DC. circuit with said workpiece and simultaneously elevating the temperature of said piece.

3. A high temperature furnace, comprising means providing an evacuated chamber, suport means for mounting a workpiece within said chamber, a tubular element of electron emissive material, mounted within said chamber and in line with said workpiece, means for delivering a flow of gas through said element, circuit means providing a DC. potential between said element and said workpiece and means for heating said element to cause ionization of said gas, ions from said gas causing further heating of said element to a point producing thermionic emission, the ionized discharge thereby completing a DC. circuit with said workpiece and simultaneously elevating the temperature of said workpiece.

References Cited by the Examiner UNITED STATES PATENTS 2,935,395 5/60 Smith 13-31 X 2,945,119 7/60 Blackman. 3,003,061 10/61 Berghaus et al. 13-31 3,076,085 1/63 Sundstrom 219 FOREIGN PATENTS 894,839 9/60 Great Britain. 866,106 4/61 Great Britain.

OTHER REFERENCES German application 1,100,200 printed Feb. 23, 1961.

RICHARD M. WOOD, Primary Examiner.

JOSEPH V. TRUHE, Examiner. 

1. A HIGH TEMPERTURE FURANCE, COMPRISING MEANS PROVIDING AN EVACUATED CHAMBER, SUPPORT MEANS FOR MOUNTING A WORKPIECE WITHIN SAID CHAMBER, AN ELECTRON EMISSIVE TUBULAR CYLINDRICAL ELEMENT MOUNTED WITHIN SAID CHAMBER AND IN LINE WITH SAID WORKPIECE, MEANS FOR DELIVERING A FLOW OF GAS THROUGH SAID ELEMENT, FIRST CIRCUIT MEANS PROVIDING AN RF CURRENT TO HEAT SAID ELEMENT FOR FIRST IONIZING SAID GAS, IONS FROM SAID IONIZED GAS CAUSING FUTHER HEATING OF SAID ELEMENT TO A POINT PRODUCING TERMIONIC EMISSION, AND SECOND CIRCUIT MEANS PROVIDING A D.C. POTENTIAL BETWEEN SAID ELEMENT AND SAID WORKPIECE TO PRODUCE A DISCHARGE OF THE IONIZED GAS, SAID IONIZED DISCHARGE THEREBY COMPLETING A D.C. CIRCUIT WITH SAID WORKPIECE AND SIMULTANEOUSLY ELEVATING THE TEMPERATURE OF SAID PIECE. 